.TH std::popcount 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::popcount \- std::popcount

.SH Synopsis
   Defined in header <bit>
   template< class T >                      \fI(since C++20)\fP
   constexpr int popcount( T x ) noexcept;

   Returns the number of 1 bits in the value of x.

   This overload participates in overload resolution only if T is an unsigned integer
   type (that is, unsigned char, unsigned short, unsigned int, unsigned long, unsigned
   long long, or an extended unsigned integer type).

.SH Parameters

   x - value of unsigned integer type

.SH Return value

   The number of 1 bits in the value of x.

.SH Notes

   The name popcount is a contraction for "population count".

   Feature-test macro  Value    Std      Feature
   __cpp_lib_bitops   201907L (C++20) Bit operations

.SH Example


// Run this code

 #include <bit>
 #include <bitset>
 #include <cstdint>
 #include <iostream>

 static_assert(std::popcount(0xFULL) == 4);

 int main()
 {
     for (const std::uint8_t x : {0, 0b00011101, 0b11111111})
         std::cout << "popcount( " << std::bitset<8>(x) << " ) = "
                   << std::popcount(x) << '\\n';
 }

.SH Output:

 popcount( 00000000 ) = 0
 popcount( 00011101 ) = 4
 popcount( 11111111 ) = 8

.SH See also

   countl_zero    counts the number of consecutive 0 bits, starting from the most
   (C++20)        significant bit
                  \fI(function template)\fP
   countl_one     counts the number of consecutive 1 bits, starting from the most
   (C++20)        significant bit
                  \fI(function template)\fP
   countr_zero    counts the number of consecutive 0 bits, starting from the least
   (C++20)        significant bit
                  \fI(function template)\fP
   countr_one     counts the number of consecutive 1 bits, starting from the least
   (C++20)        significant bit
                  \fI(function template)\fP
   has_single_bit checks if a number is an integral power of 2
   (C++20)        \fI(function template)\fP
   count          returns the number of bits set to true
                  \fI(public member function of std::bitset<N>)\fP
   all            checks if all, any or none of the bits are set to true
   any            \fI(public member function of std::bitset<N>)\fP
   none
